Steering control system and a method for controlling steering

ABSTRACT

A steering control system for a commercial vehicle having braking and steering systems. The braking system brakes dissymetrically side wheels of the vehicle. The steering system steers the vehicle based on a steering signal. The steering control system includes selection and control modules. The selection module switches between first and second steering modes. The first mode indicates steering of the vehicle by turning vehicle wheels. The second mode indicates steering of the vehicle by generating a braking signal for at least one wheel providing a yaw moment applied to the vehicle. The control module generates the first signal indicating a steering demand in the first mode and a second signal indicating a steering demand in the second mode. The control module provides the first signal to the steering system and the second signal to the braking system to brake the vehicle dissymetrically to steer the vehicle with the yaw moment.

FIELD OF THE INVENTION

The present invention relates to a steering control system and a methodfor controlling steering and, in particular, a system for controllingthe lateral movement of a vehicle using a Steer-by-Brake process.

BACKGROUND INFORMATION

Vehicles are nowadays equipped with a number of assist functions tosupport the driver in various situations. For example, a traffic jamassist function helps the driver to keep a secure distance to a vehicleahead while following the traffic lane. Such traffic jam assist functionis implemented in conventional systems only during low speed operationsas for example in stop & go situations. In these situations, however,the vehicle has to brake frequently resulting in an increased brakelining wear. In addition, in conventional systems it is difficult tofollow the traffic lane autonomously, because the autonomous actuationof the steering system, in particular for commercial vehicles, istechnically very involved.

Therefore, there is a demand of a steering control system which can beused easily, in particular, for the traffic jam situation withoutincreasing the brake lining wear.

SUMMARY OF THE INVENTION

At least some of the above-mentioned problems may be solved by asteering control system as described herein and a vehicle as describedherein, and a method for controlling steering as described herein. Thedependent claims relate to further specifically advantageousrealizations of the steering control system as described herein.

The present invention relates to a steering control system for acommercial vehicle. The commercial vehicle comprises a braking systemand a steering system, the braking system is configured to brakedissymetrically side wheels of the vehicle, and the steering system isconfigured to steer the vehicle in response to a steering signal. Thesteering control system comprises a selection module and a controlmodule. The selection module is configured to select a first steeringmode or a second steering mode, wherein the first steering mode relatesto a steering of the vehicle by turning vehicle wheels and the secondsteering mode relates to a steering of the vehicle by generating abraking signal for at least one vehicle wheel resulting in a yaw momentapplied to the vehicle. The control module is configured to generate afirst steering signal indicating a steering demand if the first steeringmode is selected and a second steering signal indicating a steeringdemand if the second steering mode is selected. The control module isfurther configured to provide the first steering signal to the steeringsystem and the second steering signal to the braking system to brake thevehicle wheels dissymetrically and thereby steer the vehicle as a resultof the generated yaw moment. For example, the front right wheel may bebraked stronger than the front left wheel (or vice versa) resulting in aright turn (or left turn).

Optionally, the selection module comprises an interface for the driverof the commercial vehicle to enable the driver to select (or switch) thefirst steering mode or the second steering mode in response to aninteraction of the driver with the interface. Thus, the driver canintentionally turn on/off the second steering mode. The switching is notperformed automatically by the vehicle as e.g. in stabilization systemsas ESP.

The commercial vehicle may be adapted to be operated in a traffic jamassistant mode (e.g. using a traffic jam assistant unit), and theselection module is optionally configured to activate the secondsteering mode in the traffic jam assistant mode. Again, the activationof the traffic jam assistant mode is done by the driver explicitly. Inthe traffic jam assistant mode, the vehicle may follow an object ahead(e.g. another vehicle) while maintaining a safe distance to the objectand staying inside a given traffic lane (and does not pass the objectahead).

The vehicle may comprise at least one sensor (e.g. a camera) to detect amisalignment of the vehicle with the traffic lane and the control moduleis optionally configured to receive a signal indicating the misalignmentand to generate, based thereon, a second steering signal to correct themisalignment and to further follow the lane. This alignment correctioncan be combined with the distant control to the object ahead, i.e. anyunsafe distance can be corrected by braking the vehicle accordingly.

The present invention is, however, not limited to the traffic assistantmode, but may also be employed in other turning operations. For example,the control module may optionally be configured to generated a secondsteering signal for performing a lane change autonomously.

In addition, the vehicle may comprise at least one sensor for detectinga vehicle ahead and the control module may be configured to generate asecond steering signal to follow the vehicle ahead.

Optionally, the vehicle may also comprise at least one braking sensorfor detecting a braking request or a deceleration of the vehicle and theselection module may be configured to switch to the second steering modein response to a detected braking signal or deceleration of the vehicle.

The present invention relates also to a vehicle with a steering controlsystem, as it was defined before. The vehicle may, in particular, be acommercial vehicle with a steering system having a positive scrub radiusto amplify steering operation when braking dissymetrically. The steeringsystem of the vehicle may comprise a steering column, which iscontrolled to be turned during steering in the first steering mode.

The present invention relates also to a method of controlling steeringfor the commercial vehicle. The commercial vehicle comprises a brakingsystem and a steering system, the braking system is configured to brakedissymetrically side wheels of the vehicle, and the steering system isconfigured to steer the vehicle in response to a steering signal. Themethod comprises the steps of:

-   -   selecting a first steering mode or a second steering mode,        wherein the first steering mode performs a steering of the        vehicle by turning vehicle wheels and the second steering mode        performs a steering of the vehicle by generating a braking        signal for at least one vehicle wheel resulting in a yaw moment        applied to the vehicle; and    -   generating a first steering signal indicating a steering demand        in the first steering mode and a second steering signal        indicating a steering demand in the second steering mode, and    -   providing the first steering signal to the steering system and        the second steering signal to the braking system to brake the        vehicle dissymetrically and thereby steer the vehicle as a        result of the generated yaw moment.

This method may also be implemented in software or a computer programproduct and the order of steps may not be important to achieve thedesired effect. Embodiments of the present invention can, in particular,be in an engine control unit or implemented by software or a softwaremodule in an ECU (electronic control unit). Therefore, embodiment relatealso to a computer program having a program code for performing themethod, when the computer program is executed on a processor.

According to the present invention the steering actuators are notactively used to control the lateral movement of the vehicle—inparticular not for steering the vehicle in special situation as theautonomous driving. Instead, according to embodiments, thesteer-by-braking function is actively employed as a regular drivingfunction. This function is not only being used as a backup system toenable a steering in case the regular steering system fails. This newnormal operation mode is especially employed during a traffic jamsituation where frequent stopping operations can be used to re-align thevehicle along a traffic lane. Hence, when the traffic jam assistantfunction is activated, the steering control system can likewise beswitched in the second steering mode to enable the steer-by-brakefunction. Further advantageous applications of embodiments of thepresent invention relate to functions as preventing a lane departure ofthe vehicle at regular cruising speed.

A particular advantage of embodiments of the present invention is thatactive steering actuators are not needed while still enabling anautonomous control of the vehicle. Since such active steering actuatorsare expensive and moreover not standard in commercial vehicles,embodiments can be easily implemented even in heavy commercial vehiclesto enable an automatic steering. This is made possible by using thebraking system to correct the orientation of the vehicle along the road.

Some examples of the system and/or methods will be described in thefollowing by way of examples only, and with respect to the accompanyingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a steering control system according to an embodiment ofthe present invention.

FIG. 2 illustrates how embodiments handle a lane following situation.

FIGS. 3A and 3B illustrate a traffic jam assist scenario.

FIG. 4 shows the architecture used for the traffic jam assist unitaccording to embodiment.

FIG. 5 shows a flow diagram of a method for controlling steering for thecommercial vehicle.

DETAILED DESCRIPTION

FIG. 1 shows a steering control system 100 suitable for a commercialvehicle, which comprises a braking system 20 and a steering system 30.The braking system 20 is able to brake dissymetrically side wheels ofthe vehicle and the steering system is able to steer the vehicle inresponse to a steering signal by turning the wheels. The steeringcontrol system 100 comprises a selection module 110 and a control module120. The control module 120 is configured to generate the first steeringsignal 111 indicating a steering demand in a first steering mode and asecond steering signal 112 indicating a steering demand in the secondsteering mode. The selection module 110 is configured to switch betweenthe first steering mode and the second steering mode, wherein the firststeering mode steers of the vehicle by turning vehicle wheels inresponse to a first steering signal 111. In the second steering mode asteering of the vehicle is achieved by generating a braking signal 21,22 for at least one vehicle wheel resulting in a yaw moment applied tothe vehicle. This yaw moment results in a rotation force and iscontrolled by the strength or degree of the dissymmetrical brakingforce.

Although FIG. 1 sows the selection module 110 between the control module120 and the steering/braking systems 20, 30, this arrangement shallillustrate only one possibility. In further embodiments the selectionmodule 110 (or part thereof) may be arranged to receive a signal fromthe control module 120 or within the control module 120 so that thecontrol module 120 is able to generate different signals based on theselected mode.

Independently of the concrete arrangement in the steering control system100, either the first steering signal 111 (in the first switching mode)or the second steering signal 112 (in the second switching mode) isgenerated. The first steering signal 111 is submitted to the steeringsystem 30 which provides an actuator signal 31 to the steering actuatorsin order to turn the steered wheels to the left or to the right (forexample using a power steering system). The second steering signal 112is provided to the braking system 20. Based on the second steeringsignal 112 the braking system 20 generates different or dissymmetricalbraking signals 21, 22, which are provided to the right wheel and leftwheel. For example, the second steering signal 112 indicate a demand fora right turn of the vehicle. As a result, the braking system 20 providesonly a braking signal 22 to the right wheel in order to perform a rightmovement of the vehicle. Of course, a strength of the dissymmetricalbraking signals 21, 22 are adjusted to perform a desired turningoperation without destabilizing the vehicle for example, by applying asharp strong braking force only on one wheel.

Embodiments implement thus the steer-by-brake (SBB) function as a normaloperation mode (comfort function) in vehicles, wherein the brakes oneach wheel are controlled separately to influence the steering of thevehicle. Embodiments may be implemented at all wheels of the vehicle.However, the most efficient steering effect may be achievable only ifthe wheels on the front axle are used for the SBB-function. A personskilled in the art will appreciate that this concept has particularadvantages for vehicles with a positive scrub radius, which results inan amplification of the steering effect in case dissymmetric (orasymmetric) friction forces apply to the left right wheels. A positivescrub radius is typically implemented in commercial vehicles, since itsupports a steering operation. Thus, embodiments of the presentinvention have particular advantages for commercial vehicles.

FIG. 2 depicts a situation, where a commercial vehicle 10 follows atraffic lane 200 and a braking force 21 is applied to the front rightwheel. As a consequence, the vehicle moves to the right as indicated bythe arrow 11. This effect can be used to keep an alignment of thevehicle 10 along the traffic lanes 200 (see left hand side in FIG. 2).For example, a deviation of the vehicle to the left-hand side can becorrected by a braking force on the right-wheel resulting in the rightmovement 11, whereas a deviation to the right-hand side can be correctedby applying a braking force on the left wheel resulting in a leftmovement 12 of the vehicle. As a result, the vehicle can automaticallystay inside the traffic lane 200 without the need to actuate activelythe steering system of the vehicle 10.

FIG. 3A and FIG. 3B illustrate the traffic jam assist scenario, whereinin FIG. 3A the vehicle 10 follows an object 210 along the traffic lane200. Again, the alignment of the vehicle 10 along the traffic lane 200can be maintained as described in FIG. 2. In FIG. 3B the vehicle 10follows the object 210 when the object 210 leaves the traffic lane 200,for example, to make a lane change. For both cases, the needed steeringoperations can be carried out using the steering control system 100.

FIG. 4 shows the architecture used for the traffic jam assist function.This architecture involves a traffic jam assist unit 300, which isconnected to one or more sensors 310, 320. For example, a radar sensor310 can measure the distance to the vehicle 210 ahead and a camerasensor 320 can keep track of the traffic lane 200 and provides a sensorsignal in the case the vehicle 10 tends to leave the traffic lane 200.This may, for example, be achieved by detecting the lane markings, whichshould be in a particular angular range, when viewed from the vehicle10, if the vehicle 10 is running in the middle of the traffic lane 200.

The sensor data of the radar sensor 310 and the exemplary camera 320 areprovided for the traffic jam assist unit 300 which is able to detect theobject 210, using the radar sensor 310, and to detect any possible lanedeparture using the exemplary camera 320. The ideal position for thevehicle 10 may, be defined using particular thresholds for the distanceto the object 210 ahead and for the angles to the traffic lane markings.Any deviation from a range of acceptable positions may trigger an actionin the traffic jam assist unit 300. For example, control signals 301,302, 303 can be generated to actuate actuators of the vehicle 10 tocorrect the position and/or alignment of the vehicle 10. The traffic jamassist unit 300 may generate an acceleration signal 301 and provide thissignal to an engine 401 in order to accelerate the vehicle 10. Thetraffic jam assist unit 300 can also generate a deceleration signal 302and send this signal to the braking system actuators 402 in order toslow down the vehicle 10. According to the present invention, thetraffic jam assist unit 300 can further generate a Steer-by-Brake signal303 and provide this signal to the braking system actuators 403 assignedto this function (e.g. the front axle wheels) to dissymmetrically brakewheels of the vehicle 10 to thereby correct the orientation of thevehicle 10.

The SBB signal 303 may be the second steering signal 112 (see FIG. 1),if the system 100 in included in the traffic jam assist unit 300. It isalso possible that the SBB signal 303 can be sent to the steeringcontrol system 100 which interprets the signal as a steering demand andgenerates, based thereon, an appropriate second steering signal 112.

FIG. 5 depicts a flow diagram of a method for controlling steering forthe commercial vehicle. The method comprises the steps of:

-   -   switching S110 between or selecting a first steering mode and a        second steering mode, wherein the first steering mode performs a        steering of the vehicle by turning vehicle wheels and the second        steering mode performs a steering of the vehicle by generating a        braking signal for at least one vehicle wheel resulting in a yaw        moment applied to the vehicle;    -   generating S120 a first steering signal indicating a steering        demand if the first steering mode is switched, and a second        steering signal indicating a steering demand if the second        steering mode is switched, and    -   providing S130 the first steering signal to the steering system        or the second steering signal to the braking system to brake the        vehicle dissymetrically and thereby steer the vehicle as a        result of the yaw moment.

This method may also be a computer-implemented method. A person of skillin the art would readily recognize that steps of various above-describedmethods may be performed by programmed computers. Embodiments are alsointended to cover program storage devices, e.g., digital data storagemedia, which are machine or computer readable and encodemachine-executable or computer-executable programs of instructions,wherein the instructions perform some or all of the acts of theabove-described methods, when executed on a computer or processor.

The advantage of embodiments of the present invention is to realize thesteering functions without the need of any additional actuator, butusing the already installed braking system. By using this system, thecontrol of the lateral movement of the vehicle can be achieved withoutmajor modifications of present or of new vehicles. It is even possiblethat older vehicle architectures can be retrofitted with the newfunction without involving high costs.

Since current vehicles do not have active steering systems, which couldsupport new functions, embodiments of the present invention can beeasily implemented in these commercial vehicles without the need ofmajor modifications.

The description and drawings merely illustrate the principles of thedisclosure. It will thus be appreciated that those skilled in the artwill be able to devise various arrangements that, although notexplicitly described or shown herein, embody the principles of thedisclosure and are included within its scope.

Furthermore, while each embodiment may stand on its own as a separateexample, it is to be noted that in other embodiments the definedfeatures can be combined differently, i.e. a particular featuredescripted in one embodiment may also be realized in other embodiments.Such combinations are covered by the disclosure herein unless it isstated that a specific combination is not intended.

The list of reference signs is as follows:

-   10 vehicle-   11,12 right/left movement-   30 steering system-   31 steering actuator signal-   20 braking system-   21,22 dissymmetrical braking signals-   100 steering control system-   110 control module-   111 first steering signal-   112 second steering signal-   120 selection module-   200 traffic lane-   300 traffic jam assistant unit-   310 radar sensor-   320 camera-   301, 302, . . . control signals of the traffic jam assistant unit-   401 engine-   402 braking system actuators-   403 braking system actuators assigned for SBB function

1-11. (canceled)
 12. A steering control system for a commercial vehicle, comprising: a selection module to select a first steering mode or a second steering mode, wherein the commercial vehicle includes a braking system and a steering system, the braking system being configured to brake dissymetrically side wheels of the vehicle, the steering system being configured to steer the vehicle in response to a steering signal, and wherein the first steering mode relates to a steering of the vehicle by turning vehicle wheels and the second steering mode relates to a steering of the vehicle by generating a braking signal for at least one vehicle wheel resulting in a yaw moment applied to the vehicle; and a control module to generate a first steering signal indicating a steering demand if the first steering mode is selected and a second steering signal indicating a steering demand if the second steering mode is selected; wherein the control module is configured to provide the first steering signal to the steering system and the second steering signal to the braking system to brake the vehicle dissymetrically and thereby steer the vehicle as a result of the yaw moment.
 13. The steering control system of claim 12, wherein the selection module includes an interface for the driver of the commercial vehicle to enable the driver to select the first steering mode or the second steering mode in response to an interaction with the interface.
 14. The steering control system of claim 12, wherein the commercial vehicle includes a traffic jam assistant unit to operate the vehicle in a traffic jam assistant mode, characterized in that the selection module is configured to activate second steering mode in the traffic jam assistant mode.
 15. The steering control system of claim 12, wherein vehicle includes at least one sensor to detect a misalignment of the vehicle with a traffic lane, characterized in that the control module is configured to receive a signal indicating the misalignment and to generate, based thereon, a second steering signal to correct the misalignment to further follow the lane.
 16. The steering control system of claim 12, wherein the control module is configured to generated a second steering signal for performing a lane change autonomously.
 17. The steering control system of claim 12, wherein the vehicle includes at least one sensor for detecting a vehicle ahead, characterized in that the control module is configured to generate a second steering signal to follow the vehicle ahead.
 18. The steering control system of claim 12, wherein the vehicle includes at least one braking sensor for detecting a braking request or a deceleration of the vehicle, characterized in that the selection module is configured to switch to the second steering mode in response to a detected braking signal or deceleration of the vehicle.
 19. A vehicle, comprising: a steering control system, including: a selection module to select a first steering mode or a second steering mode, wherein the commercial vehicle includes a braking system and a steering system, the braking system being configured to brake dissymetrically side wheels of the vehicle, the steering system being configured to steer the vehicle in response to a steering signal, and wherein the first steering mode relates to a steering of the vehicle by turning vehicle wheels and the second steering mode relates to a steering of the vehicle by generating a braking signal for at least one vehicle wheel resulting in a yaw moment applied to the vehicle; and a control module to generate a first steering signal indicating a steering demand if the first steering mode is selected and a second steering signal indicating a steering demand if the second steering mode is selected; wherein the control module is configured to provide the first steering signal to the steering system and the second steering signal to the braking system to brake the vehicle dissymetrically and thereby steer the vehicle as a result of the yaw moment.
 20. The vehicle of claim 19, wherein the vehicle is a commercial vehicle with a steering system having a positive scrub radius to amplify steering operation by dissymmetrical braking, and wherein the steering system includes a steering column which is turned during steering in the first steering mode.
 21. A method of controlling a steering for a commercial vehicle, the method comprising: selecting a first steering mode or a second steering mode, wherein the commercial vehicle includes a braking system and a steering system, the braking system being configured to brake dissymetrically side wheels of the vehicle, the steering system being configured to steer the vehicle in response to a steering signal, wherein the first steering mode indicates a steering of the vehicle by turning vehicle wheels and the second steering mode indicates a steering of the vehicle by generating a braking signal for at least one vehicle wheel resulting in a yaw moment applied to the vehicle; and generating a first steering signal indicating a steering demand in the first steering mode and a second steering signal indicating a steering demand in the second steering mode, and providing the first steering signal to the steering system and the second steering signal to the braking system to brake the vehicle dissymetrically and thereby steer the vehicle as a result of the yaw moment.
 22. A non-transitory computer readable medium having a computer program, which is executable by a processor, comprising: a program code arrangement having a program code for controlling a steering for a commercial vehicle, by performing the following: selecting a first steering mode or a second steering mode, wherein the commercial vehicle includes a braking system and a steering system, the braking system being configured to brake dissymetrically side wheels of the vehicle, the steering system being configured to steer the vehicle in response to a steering signal, wherein the first steering mode indicates a steering of the vehicle by turning vehicle wheels and the second steering mode indicates a steering of the vehicle by generating a braking signal for at least one vehicle wheel resulting in a yaw moment applied to the vehicle; and generating a first steering signal indicating a steering demand in the first steering mode and a second steering signal indicating a steering demand in the second steering mode, and providing the first steering signal to the steering system and the second steering signal to the braking system to brake the vehicle dissymetrically and thereby steer the vehicle as a result of the yaw moment. 